Chronic myelogenous leukemia
DEFINITION
Chronic myelogenous leukemia (CML) is an uncommon type of cancer of the blood cells. The term “chronic” in chronic myelogenous leukemia indicates that this cancer tends to progress more slowly than acute forms of leukemia. The term “myelogenous” (my-uh-LOHJ-uh-nus) in chronic myelogenous leukemia refers to the type of cells affected by this cancer.
Chronic myelogenous leukemia can also be called chronic myeloid leukemia and chronic granulocytic leukemia. Chronic myelogenous leukemia typically affects older adults and rarely occurs in children, though it can occur at any age.
CAUSES
Chronic myelogenous leukemia occurs when something goes awry in the genes of your blood cells. It’s not clear what initially sets off this process, but doctors have discovered how it progresses into chronic myelogenous leukemia.
First, an abnormal chromosome develops
Human cells normally contain 23 pairs of chromosomes. These chromosomes hold the DNA that contains the instructions (genes) that control the cells in your body. In people with chronic myelogenous leukemia, the chromosomes in the blood cells swap sections with each other. A section of chromosome 9 switches places with a section of chromosome 22, creating an extra-short chromosome 22 and an extra-long chromosome 9.
The extra-short chromosome 22 is called the Philadelphia chromosome, named for the city where it was discovered. The Philadelphia chromosome is present in the blood cells of 90 percent of people with chronic myelogenous leukemia.
Second, the abnormal chromosome creates a new gene
The Philadelphia chromosome creates a new gene. Genes from chromosome 9 combine with genes from chromosome 22 to create a new gene called BCR-ABL. The BCR-ABL gene contains instructions that tell the abnormal blood cell to produce too much of a protein called tyrosine kinase. Tyrosine kinase promotes cancer by allowing certain blood cells to grow out of control.
Third, the new gene allows too many diseased blood cells
Your blood cells originate in the bone marrow, a spongy material inside your bones. When your bone marrow functions normally, it produces immature cells (blood stem cells) in a controlled way. These cells then mature and specialize into the various types of blood cells that circulate in your body — red cells, white cells and platelets.
In chronic myelogenous leukemia, this process doesn’t work properly. The tyrosine kinase caused by the BCR-ABL gene causes too many white blood cells. Most or all of these contain the abnormal Philadelphia chromosome. The diseased white blood cells don’t grow and die like normal cells. The diseased white blood cells build up in huge numbers, crowding out healthy blood cells and damaging the bone marrow.
SYMPTOMS
Signs and symptoms of chronic myelogenous leukemia may include:
- Easy bleeding
- Feeling run-down or tired
- Fever
- Losing weight without trying
- Loss of appetite
- Pain or fullness below the ribs on the left side
- Pale skin
- Sweating excessively during sleep (night sweats)
When to see a doctor
- Chronic myelogenous leukemia doesn’t always reveal itself with obvious signs and symptoms during the early phase. It’s possible to live with chronic myelogenous leukemia for months or years without realizing it.
- Because people with chronic myelogenous leukemia tend to respond better to treatment when it’s started early, make an appointment with your doctor if you have any persistent signs or symptoms that worry you.
